1. Field of the Invention
The present invention relates to a solid-state image-sensing device, and more particularly, to a charge coupled device (CCD) type solid-state image sensing device.
2. Description of the Related Art
A CCD type solid-state device is typically embedded in mobile phone cameras and digital still cameras. It senses an image coming into view, converts into an electric signal, and transmits the signal to a display driving apparatus. The display driving apparatus processes signals for color image data (R, G, and B) output from the solid-state device and drives a display apparatus such as a liquid crystal display (LCD). In particular, in a system employing a CCD solid-state device, a sub-sampling mode of the solid-state device is a mode in which vertical resolution is lowered without changing the driving frequency and a full frame image signal is output. This sub-sampling mode is performed to quickly process a signal in steps that do not need a high-resolution display, such as a step for confirmation in advance before photographing a desired image, and a step for setting auto focus.
FIG. 1 shows the pixel structure of a conventional CCD solid-state image-sensing device, which is indicated generally by the reference numeral 100. Referring to FIG. 1, the conventional CCD solid state image sensing device 100 is designed to use an interlacing method, and has a pixel structure having a two-dimensionally (2D) disposed photodiode matrix 180 and a vertical CCD 170 connected to the photodiodes 180. Normally in a color solid-state device, a color filter is installed on the top of each pixel so that light of only a predetermined color can be received. In order to form color signals, at least three types of color filters are disposed. A most widely used color filter array is Bayer pattern, as used in the device 100, in which two color patterns of red (R) and green (G) are disposed in one row and two color patterns of green (G) and blue (B) are disposed in the other row and these rows are repeatedly arranged. At this time, green (G) color closely related to a luminance signal is disposed in all rows and red (R) color and blue (B) color are disposed diagonally so that luminance resolution can increase. In digital still cameras and the like, in order to increase resolution, a CCD with one million or more pixels disposed has been employed. In particular, this conventional solid-state device is designed to fit the interlacing method and the vertical CCD 170 is driven by a plurality of driving signals (V1A, V1B, V2, V3A, V3B, and V4). The general driving method of this ordinary solid-state device is shown in Japanese Patent Publication No. 2001-160924.
FIG. 2 shows a conventional 8-matrix pixel structure of the solid-state image-sensing device 100 of FIG. 1, indicated generally by the reference numeral 200. That is, although driving electrodes 110 through 160 for transferring signals (V1A, V1B, V2, V3A, V3B, and V4) driving the vertical CCD 170 are shown in FIG. 2 separated between photodiodes 180, the electrodes are overlapping each other in internally different layers of the device 100 as shown in FIG. 1. In the case of a monochrome CCD sensing only brightness of light, sub-sampling mode can be implemented by adding signals of neighboring rows and transmitting. However, in the case of a color CCD to obtain three color signals (R, G, and B), there is a constraint that signals of neighboring rows corresponding to an identical color should be added. Accordingly, in order to implement a sub-sampling mode, signals of some rows connected to V1A and V3A are output by the pixel structure and driving signals (V1A, V1B, V2, V3A, V3B, and V4) of the structure 200, through the vertical CCD 170 and horizontal CCD 190 as discussed below with respect to FIG. 3, and signals of the remaining rows are not output and are discarded.
FIG. 3 shows a conventional sub-sampling mode of operation for the solid-state image-sensing device of FIG. 2, indicated generally by the reference numeral 300. When a user takes desired pictures, usually the video signal of all pixels sensed by the photodiodes 180 are output through the vertical CCD 170 and the horizontal CCD 190. However, in the sub-sampling mode 300, vertical resolution is lowered and then the video signal is output. The exemplary operation 300 senses the video signal in only two rows of pixels among eight rows of pixels, which are selected and output with the vertical resolution lowered down to ¼. That is, first, the mechanical shutter is opened and signal charges are accumulated in the photodiodes 180 for a predetermined time. Then, if an active signal for readout is applied to the driving electrodes 110 and 140 transferring V1A and V3A among vertical driving signals, video signals of the corresponding one (R. G) row and one (G, B) row are transmitted to the vertical CCD 170, and video signals packets thus transmitted to the vertical CCD 170 are vertically transmitted by the vertical CCD driving signals (V1A, V1B, V2, V3A, V3B, and V4) from the vertical CCD 170 to the horizontal CCD 190. The horizontal CCD 190 receives transmitted video signal packets and horizontally transmits by horizontal driving signals (VH1 and VH2) so that video signals for respective rows are output sequentially.
However, in the conventional CCD solid'state image sensing device and the sub-sampling mode, in order to perform vertical sub-sampling, only video signals of predetermined rows at predetermined intervals are transferred to the vertical CCD 170, and then these are output through the vertical CCD 170 and the horizontal CCD 190 such that sub-sampling mode to lower the vertical resolution is performed. Accordingly, at this time there are video signals of rows that are not output, which cause aliasing noise in which slant lines are not smoothly displayed on the display and appear in the shape of stairs. In addition, there is a problem that by outputting only part of the generated signal charges, the dynamic range of the video signals is reduced.